Abstract: In-situ leaching uranium mining using acid solutions has a great impact on groundwater environment, leaving acid plumes in groundwater after mining activities. Effective measures should be taken to restore the water quality in mining aquifers. Natural attenuation is an economical method. But the effectiveness should be evaluated before using this remediation method. In this study, natural attenuation of an acid plume in a shutdown uranium site is simulated using reactive transport modeling method. PHT3D is used to construct the model, including advective-dispersive transport, aqueous speciation of 12 components, and precipitation-dissolution of six minerals. The model has a whole simulation time of 5 years. Simulation results show that: successive pH buffer reactions with calcite, Al(OH)3(a) and Fe(OH)3(a) create distinct geochemical zones. With the high pH environmental downstream, concentration of SO42- decreases significantly related to calcite dissolution and gypsum precipitation reactions. Most metal ion contaminants also have an attenuation process.